

    \filetitle{movsum}{Moving product pseudofunction}{modellang/movprod}

	\paragraph{Syntax}\label{syntax}

\begin{verbatim}
movprod(Expr)
movprod(Expr,K)
\end{verbatim}

\paragraph{Description}\label{description}

If the second input argument, \texttt{K}, is negative, this function
expands to the moving product of the last K periods (including the
current period), i.e.

\begin{verbatim}
((Expr)*(Expr{-1})* ... *(Expr{-(K-1)})
\end{verbatim}

where \texttt{Expr\{-N\}} derives from \texttt{Expr} and has all its
time subscripts shifted by \texttt{-N} (if specified).

If the second input argument, \texttt{K}, is positive, this function
expands to the moving product of the next K periods ahead (including the
current period), i.e.

\begin{verbatim}
((Expr)*(Expr{1})* ... *(Expr{K-1})
\end{verbatim}

If the second input argument, \texttt{K}, is not specified, the default
value -4 is used (based on the fact that most of the macroeconomic
models are quarterly).

\paragraph{Example}\label{example}

The following three lines

\begin{verbatim}
movprod(Z)
movprod(Z,-3)
movprod(X+Y{-1},2)
\end{verbatim}

will expand to

\begin{verbatim}
((Z)*(Z{-1})*(Z{-2})*(Z{-3}))
((Z)*(Z{-1})*(Z{-2}))
((X+Y{-1})*(X{1}+Y))
\end{verbatim}


